Secondary Logo

Journal Logo

Introduction to the Gut Microbiome Special Issue

Lacy, Brian E. MD, PhD1; Spiegel, Brennan MD, MSHS2

American Journal of Gastroenterology: July 2019 - Volume 114 - Issue 7 - p 1013
doi: 10.14309/ajg.0000000000000303

1Mayo Clinic, Jacksonville, Florida, USA;

2Division of Gastroenterology, Cedars-Sinai Medical Center, Los Angeles, California, USA.

Correspondence: Brian E. Lacy, MD, PhD. E-mail:

Received May 17, 2019

Accepted May 17, 2019

The human microbiome is a diverse, complicated, and poorly understood organ system. Although estimates vary, the human gut microbiome contains approximately 40 trillion microorganisms. Most of these microorganisms are bacteria (approximately 500–1,000 different bacterial species) although viral, archaeal, fungal, and protozoal communities also reside in a delicate, mutualistic relationship with colon epithelial cells. This diverse community of microorganisms plays a critical role in metabolism, gut epithelial health, the immune system, and susceptibility to disease. A significant milestone in our understanding of the human microbiome occurred in 2012 with the release of information from the National Institutes of Health-sponsored Human Microbiome Project (1). DNA sequencing of healthy volunteers identified more than 10,000 microbial species. Since then researchers have examined the effects of the gut microbiome on anxiety, depression, diabetes, chronic pulmonary diseases, obesity, and cancer (2). However, the impact of the gut microbiome on both health and disease remains in its infancy and multiple fundamental questions continue to challenge researchers. Key questions include: What role does the environment play on gut microbiome function? What is the impact of diet, medication, and stress on the gut microbiome and why does it appear to vary in different individuals? Is the microbiome affecting our brain? Or, does our brain affect our microbiome? Or is it both? Why is the microbiome so fragile in some patients and so resilient in others? And finally, what role does the gut microbiome play in liver disease and gastrointestinal disorders?

These unanswered questions, and countless others, led us to commission a special issue of The American Journal of Gastroenterology dedicated to exploring the latest in microbiome science. This issue contains a number of intriguing review articles, original research studies, and expertly written editorials that will stimulate readers at all stages of their careers. Murphy et al. provide a comprehensive review on the role of the gut microbiome and cancer in the article “The Gut Microbiota in Causation, Detection, and Treatment of Cancer”. Important changes in the gut microbiome in patients with Crohn's disease are described in a novel study by Braun and colleagues entitled “Individualized Dynamics in the Gut Microbiota Precede Crohn's Disease Flare”. The effects of a probiotic Bifidobacterium longum on brain activity are nicely described by Wang and colleagues in the article entitled “Bifidobacterium longum 1714 Strain Modulates Brain Activity of Healthy Volunteers During Social Stress”, whereas the association of chronic pancreatitis and small intestinal bacterial overgrowth is analyzed by Lee et al. in the article “In Chronic Pancreatitis, a Predictive Model for Small Intestinal Bacterial Overgrowth Influences Whether to Treat without Testing”. Finally, the issue features 2 fascinating studies that report on the role of fecal microbiota transplantation for the treatment of irritable bowel syndrome and primary sclerosing cholangitis in the articles “Fecal Microbiota Transplantation for Treatment of Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis” and “Fecal Microbiota Transplantation in Patients with Primary Sclerosing Cholangitis: A Pilot Clinical Trial”, respectively.

We believe that this special issue contains an abundance of information that will benefit clinicians and researchers of all levels of knowledge and experience. We know that you will find the information presented within this issue to be valuable for your clinical practice and the care of your patients. We hope it adds important new information to the evolving and dynamic field of microbiome science in gastroenterology and beyond.

Back to Top | Article Outline


Guarantor of the article: Brian E. Lacy, MD, PhD.

Specific author contributions: B.E.L. and B.S. wrote the article.

Funding support: None.

Potential competing interests: None.

Back to Top | Article Outline


1. The Human Microbiome Consortium. Structure, function and diversity of the healthy human microbiome. Nature 2012;486:207–14.
2. Lavelle A, Hill C. Gut microbiome in health and disease. Emerging diagnostic opportunities. Gastroenterol Clin N Am 2019;48:221–35.
© The American College of Gastroenterology 2019. All Rights Reserved.